IAEA-HypoX. A randomized multicenter study of the hypoxic radiosensitizer nimorazole concomitant with accelerated radiotherapy in head and neck squamous cell carcinoma

Radioresistance or/and radiosensitivity of head and neck squamous cell carcinoma: biological angle

OBJECTIVE

This narrative review aimed to compile and summarize clinically relevant literature in radiation therapy and to discuss the potential in radioresistant and radiosensitive head and neck squamous cell carcinoma (HNSCC).

METHODS AND MATERIALS

Google Scholar, PubMed, and the Cochrane Library were retrieved using combined key words such as "radiotherapy" and "head and neck cancer." Search strings additionally queried were "radioresistant," "radiosensitive," "head and neck region," "squamous cell carcinoma," in combination with Boolean operators 'AND' and 'OR.' Subsequently, the resulting publications were included for review of the full text.

RESULTS

Radiotherapeutic responses currently in clinical observation referred to HNSCC scoping were selected into this review. The compiled mechanisms were then detailed concerning on the clinical significance, biological characteristics, and molecular function.

CONCLUSIONS

Brachytherapy or/and external-beam radiotherapy are crucial for treating HNSCC especially the early stage patients, but in some patients with locally advanced tumors, their outcome with radiation therapy is poor due to obvious radioresistance. The curative effects mainly depend on the response to radiation therapy so an updated review is needed to optimize further applications in HNSCC radiotherapy.

A radiobiological perspective on radioresistance or/and radiosensitivity of head and neck squamous cell carcinoma

Background

This article aimed to compile and summarize clinically relevant literature in radiation therapy, and to discuss the potential in radioresistant and radiosensitive head and neck cancer.

Study Design

Narrative review.

Materials and methods

Google Scholar, PubMed and the Cochrane Library were retrieved using combined key words such as "radiotherapy" and "head and neck cancer". Search strings additionally queried were "radioresistant", "radiosensitive", "head and neck region", "squamous cell carcinoma", in combination with Boolean Operators 'AND' and 'OR'. Subsequently, the resulting publications were included for review of the full text.

Results

Radiotherapeutic response currently in clinical observation referred to HNSCC scoping were selected into this review. The compiled mechanisms were then detailed concerning on the clinical significance, biological characteristics, and molecular function.

Conclusions

Brachytherapy or/and external-beam radiotherapy are crucial for treating HNSCC, especially the early stage patients, but in patients with locally advanced tumors, their outcome with radiation therapy is poor due to obvious radioresistance. The curative effects mainly depend on the response of radiation therapy, so an updated review is needed to optimize further applications in HNSCC radiotherapy.

The Therapeutic Potential of Imidazole or Quinone-Based Compounds as Radiosensitisers in Combination with Radiotherapy for the Treatment of Head and Neck Squamous Cell Carcinoma

Simple Summary

Patients with curable head and neck cancers are usually treated with a combination of chemotherapy and radiotherapy, but they experience significant, severe side effects, which greatly affect their quality of life. Some of these patients still experience disease relapse after an intensive course of treatment due to tumours that are resistant to radiotherapy and chemotherapy because of hypoxia (lack of oxygen). In addition, some patients are not suitable for and/or are not able to have combined chemotherapy with radiotherapy due to their age or other physical conditions. Certain small-molecule drugs, which are used to treat various infections including malaria, have been shown to reduce hypoxia and thus make radiotherapy more effective. Therefore, their combination with radiotherapy could have less toxicities compared with the combination of chemotherapy with radiotherapy. Here, we discuss the promising results from preclinical work and clinical trials of these agents, and their potential use in the clinic, to reduce hypoxia and to sensitise radiotherapy. These agents could potentially be used for patients who are not suitable for combined chemotherapy and radiotherapy; they may also be used to reduce the dose of radiotherapy if able to enhance radiotherapy effect at lower dose in order to reduce toxicities while maintaining the treatment efficacy in a more personalised manner.

Abstract

The addition of platinum chemotherapy to primary radiotherapy (chemoradiation) improves survival outcomes for patients with head and neck squamous cell carcinoma (HNSCC), but it carries a high incidence of acute and long-term treatment-related complications, resulting in a poor quality of life. In addition, patients with significant co-morbidities, or older patients, cannot tolerate or do not benefit from concurrent chemoradiation. These patients are often treated with radiotherapy alone resulting in poor locoregional control and worse survival outcomes. Thus, there is an urgent need to assess other less toxic treatment modalities, which could become an alternative to chemoradiation in HNSCC. Currently, there are several promising anti-cancer drugs available, but there has been very limited success so far in replacing concurrent chemoradiation due to their low efficacy or increased toxicities. However, there is new hope that a treatment strategy that incorporates agents that act as radiosensitisers to improve the efficacy of conventional radiotherapy could be an alternative to more toxic chemotherapeutic agents. Recently, imidazole-based or quinone-based anti-malarial compounds have drawn considerable attention as potential radiosensitisers in several cancers. Here, we will discuss the possibility of using these compounds as radiosensitisers, which could be assessed as safe and effective alternatives to chemotherapy, particularly for patients with HNSCC that are not suitable for concurrent chemotherapy due to their age or co-morbidities or in metastatic settings. In addition, these agents could also be tested to assess their efficacy in combination with immunotherapy in recurrent and metastatic settings or in combination with radiotherapy and immunotherapy in curative settings.

The Role of Imaging Biomarkers to Guide Pharmacological Interventions Targeting Tumor Hypoxia

Hypoxia is a common feature of solid tumors that contributes to angiogenesis, invasiveness, metastasis, altered metabolism and genomic instability. As hypoxia is a major actor in tumor progression and resistance to radiotherapy, chemotherapy and immunotherapy, multiple approaches have emerged to target tumor hypoxia. It includes among others pharmacological interventions designed to alleviate tumor hypoxia at the time of radiation therapy, prodrugs that are selectively activated in hypoxic cells or inhibitors of molecular targets involved in hypoxic cell survival (i.e., hypoxia inducible factors HIFs, PI3K/AKT/mTOR pathway, unfolded protein response). While numerous strategies were successful in pre-clinical models, their translation in the clinical practice has been disappointing so far. This therapeutic failure often results from the absence of appropriate stratification of patients that could benefit from targeted interventions. Companion diagnostics may help at different levels of the research and development, and in matching a patient to a specific intervention targeting hypoxia. In this review, we discuss the relative merits of the existing hypoxia biomarkers, their current status and the challenges for their future validation as companion diagnostics adapted to the nature of the intervention.

Significance of Specific Oxidoreductases in the Design of Hypoxia-Activated Prodrugs and Fluorescent Turn Off–On Probes for Hypoxia Imaging

Simple Summary

Hypoxia-activated prodrugs (HAPs), selectively reduced by specific oxidoreductases under hypoxic conditions, form cytotoxic agents damaging the local cancer cells. On the basis of the reported clinical data concerning several HAPs, one can draw conclusions regarding their preclinical attractiveness and, regrettably, the low efficacy of Phase III clinical trials. Clinical failure may be explained, inter alia, by the lack of screening of patients on the basis of tumor hypoxia and low availability of specific oxidoreductases involved in HAP activation. There is surprisingly little information on the quantification of these enzymes in cells or tissues, compared to the advanced research associated with the use of HAPs. Our knowledge about the expression and activity of these enzymes in various cancer cell lines under hypoxic conditions is inadequate. Only in a few cases were researchers able to demonstrate the differences in the expression or activity of selected oxidoreductases, depending on the oxygen concentration. Additionally, it was cell line dependent. More systematic studies are required. The optical probes, based on turning on the fluorescence emission upon irreversible reduction catalyzed by the overexpressed oxidoreductases, can be helpful in this type of research. Ultimately, such sensors can estimate both the oxidoreductase activity and the degree of oxygenation in one step. To achieve this goal, their response must be correlated with the expression or activity of enzymes potentially involved in turning on their emissions, as determined by biochemical methods. In conclusion, the incorporation of biomarkers to identify hypoxia is a prerequisite for successful HAP therapies. However, it is equally important to assess the level of specific oxidoreductases required for their activation.

Abstract

Hypoxia is one of the hallmarks of the tumor microenvironment and can be used in the design of targeted therapies. Cellular adaptation to hypoxic stress is regulated by hypoxia-inducible factor 1 (HIF-1). Hypoxia is responsible for the modification of cellular metabolism that can result in the development of more aggressive tumor phenotypes. Reduced oxygen concentration in hypoxic tumor cells leads to an increase in oxidoreductase activity that, in turn, leads to the activation of hypoxia-activated prodrugs (HAPs). The same conditions can convert a non-fluorescent compound into a fluorescent one (fluorescent turn off–on probes), and such probes can be designed to specifically image hypoxic cancer cells. This review focuses on the current knowledge about the expression and activity of oxidoreductases, which are relevant in the activation of HAPs and fluorescent imaging probes. The current clinical status of HAPs, their limitations, and ways to improve their efficacy are briefly discussed. The fluorescence probes triggered by reduction with specific oxidoreductase are briefly presented, with particular emphasis placed on those for which the correlation between the signal and enzyme expression determined with biochemical methods is achievable.

Tumor penetrating peptide iRGD enhances radiotherapy efficacy through reducing tumor hypoxia

Resistance to irradiation (IR) remains a major therapeutic challenge in tumor radiotherapy. The development of novel tumor‐specific radiosensitizers is crucial for effective radiotherapy against solid tumors. Here, we revealed that remodeling tumor tissue penetration via tumor‐penetrating peptide internalizing arginine–glycine–aspartic acid RGD (iRGD) enhanced irradiation efficacy. The growth of 4T1 and CT26 multicellular tumor spheroids (MCTS) and tumors was delayed significantly by the treatment with IR and iRGD. Mechanistically, iRGD reduced hypoxia in MCTS and tumors, resulting in enhanced apoptosis after MCTS and tumors were treated with IR and iRGD. This is the first report that shows enhanced radiation efficacy by remodeling tumor‐specific tissue penetration with iRGD, implying the potential clinical application of peptides in future tumor therapy.

Hypoxic gene expression is a prognostic factor for disease free survival in a cohort of locally advanced squamous cell cancer of the uterine cervix

INTRODUCTION

Tumour hypoxia in locally advanced squamous cervical cancer (LACC) has been shown to be of substantial prognostic importance. The aims of the present study were therefore to investigate if hypoxia could be identified by a newly validated hypoxic gene expression classifier and used as a prognostic factor for disease free survival (DFS).

MATERIAL AND METHODS

Paraffin embedded biopsies were obtained from 190 patients with LACC with squamous cell carcinoma treated 2005-2016 with chemo-radiation and image guided adaptive brachytherapy. Analysis of hypoxia was successful in 183 patients (96%). Hypoxic classification of tumours into 'more' or 'less' hypoxic was based on 15 genes using the same method as in a prospective head and neck cancer trial (NCT02661152). HPV was genotyped using INNO-LiPA. Local tumour invasion was evaluated by the T-score. Primary endpoint was DFS analysed by Kaplan-Meier and Cox regression. Events were death of any cause, persistent disease, or recurrence.

RESULTS

The FIGO₂₀₀₉ stage distribution was IB-IIA 9%, IIB 64%, and III-IVA 27%, and mean T-score was 7.2. Pathological nodes were present in 53%. Median observation time was 5.2 years. Local control rate at 5 years was 96%, and pelvic (loco-regional) control 91%. Overall, 36% of the tumours were classified as 'more' hypoxic. The frequency of 'more' hypoxic tumours increased with local tumour intrusion (30% for T-score 0-9 vs. 55% for T-score ≥10, p = 0.004). Hypoxia was associated with decreased DFS in univariate, HR 1.71 (1.04-2.82), and multivariate analysis, HR 1.75 (1.04-2.92), and the effect was particularly observed among tumours with a T-score ≥10. HPV 16/18 was not associated with improved DFS in neither in univariate nor in multivariate analysis.

CONCLUSION

Hypoxic gene expression is a prominent prognostic factor for DFS in LACC with SCC histology and should be considered for treatment stratification in clinical trials.

Interfering with Tumor Hypoxia for Radiotherapy Optimization

Hypoxia in solid tumors is an important predictor of treatment resistance and poor clinical outcome. The significance of hypoxia in the development of resistance to radiotherapy has been recognized for decades and the search for hypoxia-targeting, radiosensitizing agents continues. This review summarizes the main hypoxia-related processes relevant for radiotherapy on the subcellular, cellular and tissue level and discusses the significance of hypoxia in radiation oncology, especially with regard to the current shift towards hypofractionated treatment regimens. Furthermore, we discuss the strategies to interfere with hypoxia for radiotherapy optimization, and we highlight novel insights into the molecular pathways involved in hypoxia that might be utilized to increase the efficacy of radiotherapy.

[The role of chemoradiotherapy in curative treatment of head and neck cancer]

Radiotherapy and chemotherapy are integral parts of definitive and adjuvant therapy in the treatment of head and neck squamous cell carcinoma (HNSCC). The outcome of therapy is essentially dependent on selection and dosage of chemotherapeutical substances and on the other hand on the radiotherapeutical setting concerning fractionation, time of therapy and technical aspects. Immunotherapeutical substances have an increasing role in the therapy of HNSCC as well as particle therapy is investigated as part of radiotherapy in actual studies. Further challenges relate to treatment of HPV-induced tumors with regard to their differences in tumor biology and consecutively better prognosis.

Dual role of ER stress in response to metabolic co-targeting and radiosensitivity in head and neck cancer cells

Arginine deprivation therapy (ADT) is a new metabolic targeting approach with high therapeutic potential for various solid cancers. Combination of ADT with low doses of the natural arginine analog canavanine effectively sensitizes malignant cells to irradiation. However, the molecular mechanisms determining the sensitivity of intrinsically non-auxotrophic cancers to arginine deficiency are still poorly understood. We here show for the first time that arginine deficiency is accompanied by global metabolic changes and protein/membrane breakdown, and results in the induction of specific, more or less pronounced (severe vs. mild) ER stress responses in head and neck squamous cell carcinoma (HNSCC) cells that differ in their intrinsic ADT sensitivity. Combination of ADT with canavanine triggered catastrophic ER stress via the eIF2α-ATF4(GADD34)-CHOP pathway, thereby inducing apoptosis; the same signaling arm was irrelevant in ADT-related radiosensitization. The particular strong supra-additive effect of ADT, canavanine and irradiation in both intrinsically more and less sensitive cancer cells supports the rational of ER stress pathways as novel target for improving multi-modal metabolic anti-cancer therapy.

The Importance of the Tumor Microenvironment and Hypoxia in Delivering a Precision Medicine Approach to Veterinary Oncology

Treating individual patients on the basis of specific factors, such as biomarkers, molecular signatures, phenotypes, environment, and lifestyle is what differentiates the precision medicine initiative from standard treatment regimens. Although precision medicine can be applied to almost any branch of medicine, it is perhaps most easily applied to the field of oncology. Cancer is a heterogeneous disease, meaning that even though patients may be histologically diagnosed with the same cancer type, their tumors may have different molecular characteristics, genetic mutations or tumor microenvironments that can influence prognosis or treatment response. In this review, we describe what methods are currently available to clinicians that allow them to monitor key tumor microenvironmental parameters in a way that could be used to achieve precision medicine for cancer patients. We further describe exciting novel research involving the use of implantable medical devices for precision medicine, including those developed for mapping tumor microenvironment parameters (e.g., O₂, pH, and cancer biomarkers), delivering local drug treatments, assessing treatment responses, and monitoring for recurrence and metastasis. Although these research studies have predominantly focused on and were tailored to humans, the results and concepts are equally applicable to veterinary patients. While veterinary clinical studies that have adopted a precision medicine approach are still in their infancy, there have been some exciting success stories. These have included the development of a receptor tyrosine kinase inhibitor for canine mast cell tumors and the production of a PCR assay to monitor the chemotherapeutic response of canine high-grade B-cell lymphomas. Although precision medicine is an exciting area of research, it currently has failed to gain significant translation into human and veterinary healthcare practices. In order to begin to address this issue, there is increasing awareness that cross-disciplinary approaches involving human and veterinary clinicians, engineers and chemists may be needed to help advance precision medicine toward its full integration into human and veterinary clinical practices.

Moderately accelerated intensity-modulated radiation therapy using simultaneous integrated boost: Practical reasons or evidence-based choice? A critical appraisal of literature

Concurrent chemo-radiotherapy is the non-surgical mainstay of treatment for locally advanced head and neck squamous cell carcinoma (HNSCC). The following aspects have emerged as fundamental components of the combined approach: first, intensity modulated radiotherapy (IMRT) is the minimum standard technical requirement, with level 1 evidence in support of its reduction of late treatment-induced morbidity in comparison with 3D conformal radiotherapy. Second, cisplatin-based chemotherapy is the preferred systemic agent to be associated with radiation, with 100 mg/m² every 3 weeks deemed as the reference schedule. Because of significant progress in irradiation techniques achieved in last 15 years, the optimal fractionation schedule in modern radiation era remains controversial, especially for locally advanced disease. The purpose of this work was to perform a critical review on the value of moderately accelerated IMRT using simultaneous-integrated boost (SIB) in HNSCC, aiming to provide insights on current clinical practice and directions for future research.

Pretreatment hemoglobin level as a prognostic factor in patients with locally advanced head and neck squamous cell carcinoma

Aim

Evaluate pretreatment hemoglobin values as a prognostic factor in patients with locally advanced head and neck squamous cell carcinoma treated with concurrent chemoradiotherapy.

Background

Anemia is one of the most prevalent laboratory abnormalities in oncological disease. It leads to a decrease in cellular oxygen supply, altering radiosensitivity of tumor cells and compromising therapeutic outcomes.

Materials and Methods

Retrospective evaluation of patients with HNSCC treated with cCRT. Primary and secondary endpoint was to evaluate the correlation of Hb levels (≥12.5 g/dL or <12.5 g/dL) at the beginning of cCRT with overall survival (OS) and progression-free survival (PFS), respectively.

Results

A total of 108 patients were identified. With a median follow-up of 16.10 months median OS was 59.70 months for Hb ≥12.5 g/dL vs. 14.13 months for Hb <12.5 g/dL (p = 0.004). PFS was 12.29 months for Hb ≥12.5 g/dL and 1.68 months for Hb <12.5 g/dL (p = 0.016).

Conclusions

In this analysis, Hb ≥12.5 g/dL correlated with significantly better OS and PFS. Further studies are needed to validate these findings.

Radiobiology of stereotactic ablative radiotherapy (SABR): perspectives of clinical oncologists

Stereotactic ablative radiotherapy (SABR) is a novel radiation treatment method that delivers an intense dose of radiation to the treatment targets with high accuracy. The excellent local control and tolerance profile of SABR have made it become an important modality in cancer treatment. The radiobiology of SABR is a key factor in understanding and further optimizing the benefits of SABR. In this review, we have addressed several issues in the radiobiology of SABR from the perspective of clinical oncologists. The appropriateness of the linear-quadratic (LQ) model for SABR is controversial based on preclinical data, but it is a reliable tool from the perspective of clinical application because the biological effective dose (BED) calculated with it can represent the tumor control probability (TCP). Hypoxia is a common phenomenon in SABR in spite of the relatively small tumor size and has a negative effect on the efficacy of SABR. Preliminary studies indicate that a hypoxic radiosensitizer combined with SABR may be a feasible strategy, but so far there is not adequate evidence to support its application in routine practice. The vascular change of endothelial apoptosis and blood perfusion reduction in SABR may enhance the response of tumor cells to radiation. Combination of SABR with anti-angiogenesis therapy has shown promising efficacy and good tolerance in advanced cancers. SABR is more powerful in enhancing antitumor immunity and works better with immune checkpoint inhibitors (ICIs) than conventional fractionation radiotherapy. Combination of SABR with ICIs has become a practical option for cancer patients with metastases.

Perspective: Do Fasting, Caloric Restriction, and Diets Increase Sensitivity to Radiotherapy? A Literature Review

Caloric starvation, as well as various diets, has been proposed to increase the oxidative DNA damage induced by radiotherapy (RT). However, some diets could have dual effects, sometimes promoting cancer growth, whereas proposing caloric restriction may appear counterproductive during RT considering that the maintenance of weight is a major factor for the success of this therapy. A systematic review was performed via a PubMed search on RT and fasting, or caloric restriction, ketogenic diet (>75% of fat-derived energy intake), protein starvation, amino acid restriction, as well as the Warburg effect. Twenty-six eligible original articles (17 preclinical studies and 9 clinical noncontrolled studies on low-carbohydrate, high-fat diets popularized as ketogenic diets, representing a total of 77 patients) were included. Preclinical experiments suggest that a short period of fasting prior to radiation, and/or transient caloric restriction during treatment course, can increase tumor responsiveness. These regimens promote accumulation of oxidative lesions and insufficient repair, subsequently leading to cancer cell death. Due to their more flexible metabolism, healthy cells should be less sensitive, shifting their metabolism to support survival and repair. Interestingly, these regimens might stimulate an acute anticancer immune response, and may be of particular interest in tumors with high glucose uptake on positron emission tomography scan, a phenotype associated with poor survival and resistance to RT. Preclinical studies with ketogenic diets yielded more conflicting results, perhaps because cancer cells can sometimes metabolize fatty acids and/or ketone bodies. Randomized trials are awaited to specify the role of each strategy according to the clinical setting, although more stringent definitions of proposed diet, nutritional status, and consensual criteria for tumor response assessment are needed. In conclusion, dietary interventions during RT could be a simple and medically economical and inexpensive method that may deserve to be tested to improve efficiency of radiation.

Methodological Development of Combination Drug and Radiotherapy in Basic and Clinical Research

Newer technical improvements in radiation oncology have been rapidly implemented in recent decades, allowing an improved therapeutic ratio. The development of strategies using local and systemic treatments concurrently, mainly targeted therapies, has however plateaued. Targeted molecular compounds and immunotherapy are increasingly being incorporated as the new standard of care for a wide array of cancers. A better understanding of possible prior methodology issues is therefore required and should be integrated into upcoming early clinical trials including individualized radiotherapy-drug combinations. The outcome of clinical trials is influenced by the validity of the preclinical proofs of concept, the impact on normal tissue, the robustness of biomarkers and the quality of the delivery of radiation. Herein, key methodological aspects are discussed with the aim of optimizing the design and implementation of future precision drug-radiotherapy trials.

Prognostic value of a 15-gene hypoxia classifier in oropharyngeal cancer treated with accelerated chemoradiotherapy

PURPOSE

A 15-gene hypoxia classifier has been developed and validated as a predictive factor for patients with head and neck squamous cell carcinoma treated with radiotherapy and nimorazole. This paper aimed to investigate the role of this hypoxia classifier as a prognostic factor for patients with oropharyngeal cancer (OPC) treated with accelerated chemoradiotherapy.

METHODS

P16 and 15-gene hypoxia classifier status, categorising tumours as more or less hypoxic, were determined for 136 OPC patients. Locoregional recurrence rate (LRR) and overall survival (OS) were estimated with cumulative incidence function and Kaplan-Meier method, respectively, stratified according to p16 and hypoxia status.

RESULTS

P16-positive patients (34.6%) had significantly better LRR and OS than p16-negative patients. The 5‑year LRR of patients with more hypoxic OPC was similar to those with less hypoxic OPC in the overall patient population (27.3% versus 25.1%; p = 0.98; HR = 1.01 [CI95% 0.47;2.17]) and in the p16-negative OPC (36.4% versus 30.1%; p = 0.70; HR = 1.17 [CI95% 0.53;2.56]). No significant OS differences could be observed in neither p16-negative nor p16-positive subgroup with a 5-year OS for p16-negative more hypoxic OPC of 44.2% versus 49.0% in the less hypoxic OPC (p = 0.92; HR 0.97 [CI95% 0.51;1.84]).

CONCLUSION

No significant outcome differences were observed between more or less hypoxic tumours, as determined by the 15-gene hypoxia classifier. These results suggest that the 15-gene hypoxia classifier may not have prognostic value in an OPC patient cohort treated with accelerated chemoradiotherapy.

Overcoming Radioresistance: Small Molecule Radiosensitisers and Hypoxia-activated Prodrugs

The role of hypoxia in radiation resistance is well established and many approaches to overcome hypoxia in tumours have been explored, with variable success. Two small molecule strategies for targeting hypoxia have dominated preclinical and clinical efforts. One approach has been the use of electron-affinic nitroheterocycles as oxygen-mimetic sensitisers. These agents are best exemplified by the 5-nitroimidazole nimorazole, which has limited use in conjunction with radiotherapy in head and neck squamous cell carcinoma. The second approach seeks to leverage tumour hypoxia as a tumour-specific address for hypoxia-activated prodrugs. These prodrugs are selectively activated by reductases under hypoxia to release cytotoxins, which in some instances may diffuse to kill surrounding oxic tumour tissue. A number of these hypoxia-activated prodrugs have been examined in clinical trial and the merits and shortcomings of recent examples are discussed. There has been an evolution from delivering DNA-interactive cytotoxins to molecularly targeted agents. Efforts to implement these strategies clinically continue today, but success has been elusive. Several issues have been identified that compromised these clinical campaigns. A failure to consider the extravascular transport and the micropharmacokinetic properties of the prodrugs has reduced efficacy. One key element for these 'targeted' approaches is the need to co-develop biomarkers to identify appropriate patients. Hypoxia-activated prodrugs require biomarkers for hypoxia, but also for appropriate activating reductases in tumours, as well as markers of intrinsic sensitivity to the released drug. The field is still evolving and changes in radiation delivery and the impact of immune-oncology will provide fertile ground for future innovation.

HPV, hypoxia and radiation response in head and neck cancer

Over the last decades, the incidence of human papilloma virus (HPV) positive head and neck squamous-cell carcinoma (HNSCC) has significantly increased. Infection with high-risk HPV types drives tumourigenesis through expression of the oncoproteins E6 and E7. Currently, the primary treatment of HNSCC consists of radiotherapy, often combined with platinum-based chemotherapeutics. One of the common features of HNSCC is the occurrence of tumour hypoxia, which impairs the efficacy of radiotherapy and is a negative prognostic factor. Therefore, it is important to detect and quantify the severity of hypoxia, as well as develop strategies to specifically target hypoxic tumours. HPV-positive tumours are remarkably radiosensitive compared to HPV-negative tumours and consequently the HPV-positive patients have a better prognosis. This provides an opportunity to elucidate mechanisms of radiation sensitivity, which may reveal targets for improved therapy for HPV-negative head and neck cancers. In this review, we will discuss the differences between HPV-positive and HPV-negative head and neck tumours and methods of hypoxia detection and targeting in these disease types. Particular emphasis will be placed on the mechanisms by which HPV infection impacts radiosensitivity.

Correlation of hypoxia status with radiosensitizing effects of sodium glycididazole: A preclinical study

The correlation of pretreatment hypoxia status with the radiosensitization effect of sodium glycididazole (CMNa) was not previously defined. The purpose of the present study was to evaluate the tumor hypoxia status in various cancer xenografts and to investigate the correlation between tumor hypoxia status and radiosensitizing effects of CMNa based on the pharmacokinetic and pharmacodynamic parameters. Human esophageal cancer (EC109), head and neck cancer (FaDu) and lung cancer (A549) nude mice xenografts were used. The concentrations of CMNa and its metabolites in the tumors and normal tissues were determined by high-performance liquid chromatography following intravenous injection of 171.9, 57.3 or 19.1 mg/kg CMNa. The tumors were irradiated with 30 Gy in 6 fractions with CMNa administration prior to each irradiation. The tumor growth delay values were calculated for each treatment group and compared with groups treated with radiation alone. Tumor hypoxia status was verified by immunohistostaining of tissues for hypoxia inducible factor 1α (HIF-1α) staining, and the concentration of plasma osteopontin (OPN) was determined using ELISA. The correlation between OPN concentration and tumor growth delay was subsequently analyzed. It was observed that the drug concentration in the tumor was 1.6-2.8 times higher compared with adjacent muscle, particularly at high and medium doses. CMNa was able to sensitize tumors to irradiation, particularly for EC109 and FaDu xenografts at high dose (P<0.05). Furthermore, there was markedly increased expression of HIF-1α and plasma OPN levels in FaDu and EC109 xenografts compared with A549. Additionally, it was indicated that pretreatment hypoxia status might be correlated with the radiosensitizing effects of CMNa. The present data demonstrated that tumor hypoxia status might be correlated with the radiosensitizing effects of CMNa in different tumor models.

Targeting Hypoxia to Improve Non-Small Cell Lung Cancer Outcome

Oxygen deprivation (hypoxia) in non-small cell lung cancer (NSCLC) is an important factor in treatment resistance and poor survival. Hypoxia is an attractive therapeutic target, particularly in the context of radiotherapy, which is delivered to more than half of NSCLC patients. However, NSCLC hypoxia-targeted therapy trials have not yet translated into patient benefit. Recently, early termination of promising evofosfamide and tarloxotinib bromide studies due to futility highlighted the need for a paradigm shift in our approach to avoid disappointments in future trials. Radiotherapy dose painting strategies based on hypoxia imaging require careful refinement prior to clinical investigation. This review will summarize the role of hypoxia, highlight the potential of hypoxia as a therapeutic target, and outline past and ongoing hypoxia-targeted therapy trials in NSCLC. Evidence supporting radiotherapy dose painting based on hypoxia imaging will be critically appraised. Carefully selected hypoxia biomarkers suitable for integration within future NSCLC hypoxia-targeted therapy trials will be examined. Research gaps will be identified to guide future investigation. Although this review will focus on NSCLC hypoxia, more general discussions (eg, obstacles of hypoxia biomarker research and developing a framework for future hypoxia trials) are applicable to other tumor sites.

Targeting the AKT pathway: Repositioning HIV protease inhibitors as radiosensitizers

Cellular resistance in tumour cells to different therapeutic approaches has been a limiting factor in the curative treatment of cancer. Resistance to therapeutic radiation is a common phenomenon which significantly reduces treatment options and impacts survival. One of the mechanisms of acquiring resistance to ionizing radiation is the overexpression or activation of various oncogenes like the EGFR (epidermal growth factor receptor), RAS (rat sarcoma) oncogene or loss of PTEN (phosphatase and tensin homologue) which in turn activates the phosphatidyl inositol 3-kinase/protein kinase B (PI3-K)/AKT pathway responsible for radiation resistance in various tumours. Blocking the pathway enhances the radiation response both in vitro and in vivo. Due to the differential activation of this pathway (constitutively activated in tumour cells and not in the normal host cells), it is an excellent candidate target for molecular targeted therapy to enhance radiation sensitivity. In this regard, HIV protease inhibitors (HPIs) known to interfere with PI3-K/AKT signaling in tumour cells, have been shown to sensitize various tumour cells to radiation both in vitro and in vivo. As a result, HPIs are now being investigated as possible radiosensitizers along with various chemotherapeutic drugs. This review describes the mechanisms by which PI3-K/AKT pathway causes radioresistance and the role of HIV protease inhibitors especially nelfinavir as a potential candidate drug to target the AKT pathway for overcoming radioresistance and its use in various clinical trials for different malignancies.

Molecular targeting of hypoxia in radiotherapy

Hypoxia (low O₂) is an essential microenvironmental driver of phenotypic diversity in human solid cancers. Hypoxic cancer cells hijack evolutionarily conserved, O₂- sensitive pathways eliciting molecular adaptations that impact responses to radiotherapy, tumor recurrence and patient survival. In this review, we summarize the radiobiological, genetic, epigenetic and metabolic mechanisms orchestrating oncogenic responses to hypoxia. In addition, we outline emerging hypoxia- targeting strategies that hold promise for individualized cancer therapy in the context of radiotherapy and drug delivery.

Nanoparticles for radiooncology: Mission, vision, challenges

Cancer is one of the leading non-communicable diseases with highest mortality rates worldwide. About half of all cancer patients receive radiation treatment in the course of their disease. However, treatment outcome and curative potential of radiotherapy is often impeded by genetically and/or environmentally driven mechanisms of tumor radioresistance and normal tissue radiotoxicity. While nanomedicine-based tools for imaging, dosimetry and treatment are potential keys to the improvement of therapeutic efficacy and reducing side effects, radiotherapy is an established technique to eradicate the tumor cells. In order to progress the introduction of nanoparticles in radiooncology, due to the highly interdisciplinary nature, expertise in chemistry, radiobiology and translational research is needed. In this report recent insights and promising policies to design nanotechnology-based therapeutics for tumor radiosensitization will be discussed. An attempt is made to cover the entire field from preclinical development to clinical studies. Hence, this report illustrates (1) the radio- and tumor-biological rationales for combining nanostructures with radiotherapy, (2) tumor-site targeting strategies and mechanisms of cellular uptake, (3) biological response hypotheses for new nanomaterials of interest, and (4) challenges to translate the research findings into clinical trials.

Validation of a 15-gene hypoxia classifier in head and neck cancer for prospective use in clinical trials

BACKGROUND

In head and neck squamous cell carcinomas (HNSCC) hypoxic radioresistance can be reduced by use of the hypoxic modifier nimorazole, as shown in the DAHANCA 5 trial. Recently, a 15-gene hypoxia classifier has shown predictive impact for the effect of nimorazole by identifying 'more' and 'less' hypoxic tumors in the DAHANCA 5 cohort. A prospective multicentre EORTC-1219 study is initiated, where nimorazole and prospective use of the classifier as a predictor is tested in relation to the most recent accelerated chemoradiotherapy treatment. Validation of the gene expression classification procedures is described here.

MATERIAL AND METHODS

Formalin-fixed paraffin-embedded (FFPE) tumor material from three recent HNSCC cohorts [DAHANCA 18 (n = 96), 24 (n = 40), and IAEA Hypo (n = 55)] was used to establish and validate procedures for prospective classification of patients. Repeatability was tested for the different steps in the gene expression analysis, and reproducibility was tested with xenograft tumors (FaDu_DD, UTSCC33), where gene expression in complementary sections was compared after fixation and embedding locally and at international institutions, respectively. Intra-tumor heterogeneity was addressed by classifying biopsy samples from HNSCC tumors, where 2-4 biopsies from each tumor was accessible.

RESULTS

Procedures were successfully established for individual classification of HNSCC patients in retrospective and prospective cohorts. Measurements of gene expression levels were reproducible between different international institutions.

CONCLUSION

Technical validation of the 15-gene hypoxia classifier demonstrated that it is suitable for implementation in prospective clinical trials.

Targeting hypoxia to overcome radiation resistance in head & neck cancers: real challenge or clinical fairytale?

INTRODUCTION

Tumor hypoxia is a major cause for failure of therapy in patients with inoperable head and neck cancers.

AREAS COVERED

Various anti-hypoxic treatment strategies (e.g. hyperbaric oxygenation, hypoxic cell sensitizers) have been tested in clinical trials in head and neck cancer over the past 30 years and have shown modest improvements in combination with radiotherapy in meta-analyses. Anemia worsens tumor hypoxia, but anemia correction had no significant effect. New approaches (e.g. anti-HIF-directed molecular therapies) have just entered early clinical studies and data are lacking. Expert commentary: A new attractive and promising approach derives from recent advances in imaging and radiotherapy delivery. Progress in imaging of hypoxia (e.g. by positron emission tomography) can select patients for specific therapies and may, in particular, facilitate anti-hypoxia-directed radiotherapy which has become feasible with advanced radiotherapy techniques (IMRT with 'dose-painting'). The combination of both methods may offer a powerful tool for effective targeting of hypoxia in the near future.

Integrative Analysis of DCE-MRI and Gene Expression Profiles in Construction of a Gene Classifier for Assessment of Hypoxia-Related Risk of Chemoradiotherapy Failure in Cervical Cancer

PURPOSE

A 31-gene expression signature reflected in dynamic contrast enhanced (DCE)-MR images and correlated with hypoxia-related aggressiveness in cervical cancer was identified in previous work. We here aimed to construct a dichotomous classifier with key signature genes and a predefined classification threshold that separated cervical cancer patients into a more and less hypoxic group with different outcome to chemoradiotherapy.

EXPERIMENTAL DESIGN

A training cohort of 42 patients and two independent cohorts of 108 and 131 patients were included. Gene expression data were generated from tumor biopsies by two Illumina array generations (WG-6, HT-12). Technical transfer of the classifier to a reverse transcription quantitative PCR (RT-qPCR) platform was performed for 74 patients. The amplitude ABrix in the Brix pharmacokinetic model was extracted from DCE-MR images of 64 patients and used as an indicator of hypoxia.

RESULTS

Classifier candidates were constructed by integrative analysis of ABrix and gene expression profiles in the training cohort and evaluated by a leave-one-out cross-validation approach. On the basis of their ability to separate patients correctly according to hypoxia status, a 6-gene classifier was identified. The classifier separated the patients into two groups with different progression-free survival probability. The robustness of the classifier was demonstrated by successful validation of hypoxia association and prognostic value across cohorts, array generations, and assay platforms. The prognostic value was independent of existing clinical markers, regardless of clinical endpoints.

CONCLUSIONS

A robust DCE-MRI-associated gene classifier has been constructed that may be used to achieve an early indication of patients' risk of hypoxia-related chemoradiotherapy failure. Clin Cancer Res; 22(16); 4067-76. ©2016 AACR.

Next-generation sequencing: hype and hope for development of personalized radiation therapy?

The introduction of next-generation sequencing (NGS) in the field of cancer research has boosted worldwide efforts of genome-wide personalized oncology aiming at identifying predictive biomarkers and novel actionable targets. Despite considerable progress in understanding the molecular biology of distinct cancer entities by the use of this revolutionary technology and despite contemporaneous innovations in drug development, translation of NGS findings into improved concepts for cancer treatment remains a challenge. The aim of this article is to describe shortly the NGS platforms for DNA sequencing and in more detail key achievements and unresolved hurdles. A special focus will be given on potential clinical applications of this innovative technique in the field of radiation oncology.